Earthquake Prone Building user guide

New Zealand has a relatively high earthquake risk so it is important for safety reasons that buildings are built or upgraded to meet a minimum structural strength.

Below is a user guide for the Nelson city area for making earthquake prone buildings safer.

The law

All councils in New Zealand are required by the Building Act 2004 to have a policy on earthquake-prone, dangerous and insanitary buildings. Nelson City Council adopted its policy in May 2006 and it is overseen by the Council’s Building Unit. This brochure outlines the regulations.

The aim of the Building Act 2004 is to reduce the risks earthquakes pose to people and to buildings. The Act defines an earthquake prone building.

The City Council’s earthquake prone buildings policy was adopted after public consultation. It follows procedures for the evaluation of buildings from the New Zealand Society for Earthquake Engineering’s Guidelines for ‘Assessment and Improvement of the Structural Performance of Buildings in Earthquakes’. The policy adopts a staged approach to reducing earthquake risk, starting with identifying buildings that may be earthquake prone, and informing owners of their obligations. It balances the need to reduce risks against economic and social constraints. Administering the policy is a regulatory function of the Council in it's role as Territorial and Building Consent Authority. It is carried out by the Council's Building Unit.

Nelson City Council’s Chief Executive announced in March 2014 that buildings identified as earthquake prone will only be required to be strengthened to no less than 34% NBS. Read about this change.

Buildings affected

The policy applies to all buildings except:

  • single storey residential buildings and
  • two (or more) storey residential buildings that contain only one or two household units.

Buildings designed after 1976 are unlikely to be earthquake prone unless they have a critical structural weakness from a design deficiency or unauthorised alteration.

eqp5

eqp4

The Process

The council is reviewing the city’s building stock to assess buildings that may be earthquake prone. If your building falls into this category you will need to engage a chartered professional engineer to complete an Initial Seismic Assessment (ISA) as set out in the NZSEE Guidelines. Owners have 12 months to get their evaluation back to Council.

Alteration

If you are applying for a building consent for an alteration, you will need an Initial Seismic Assessment from a chartered professional engineer. If the assessment shows the building is potentially earthquake prone (potentially high risk), then you’ll need a Detailed Assessment. Consent applications for buildings confirmed as earthquake prone must include an upgrade to at least 34% of the current new building standard (section 112 of the Building Act).

For more information on preparing a consent application for alterations to commercial buildings refer to alterations to existing buildings

Change of Use

If your building consent application is for a change of use, you will need a Detailed Seismic Assessment, and the building must be made to comply as nearly as is reasonably practicable with current new building standards (section 115 of the Building Act). This applies to all buildings regardless of their earthquake status.

For more information on preparing a consent application that involves a change of use refer to change of use of existing buildings

Priorities and Timeframes

Priority 1 to 3 buildings have been identified and assessments are ongoing.  Identification of priority 4 buildings is in progress.

Priority timeframes for risk reduction by building type

Priority

Type of building

Example

Timeframe for risk reduction

1

Special post-disaster functions

Hospital, civil defence

15 years

2

Crowds or high value contents

School, stadium

20 years

3

Heritage classification A or B

Historically significant buildings

25 years

4

Normal or low hazard

Most buildings

30 years

Actual time limits specified on Notices issued will account for risks identified on a case by case basis.  These have been typically in the range 10 to 20 years.

We encourage all owners to consider their options early, and to discuss possible strategies with the Council.

Damage to buildings

People are the first concern of these regulations, with damage to the building and contents a secondary consideration. Even buildings that are assessed as acceptable, or are strengthened, could still be damaged beyond repair by a significant earthquake. You should consider the insurance and business aspects of any upgrade in your long term plans, especially when you’re looking at major alterations or refurbishments.

Making the grade

NZSEE assessments will give a seismic grade to buildings, rating their expected earthquake performance.

Definitions

Earthquake risk building: resistance to earthquake attack is less than two thirds the standard of an equivalent new building (< 67%NBS). These are moderate risk buildings estimated to pose 5 to 10 times the risk of buildings complying with current building standards. There is no need to upgrade unless the owner is applying for a change of use.

Earthquake prone building: resistance to earthquake is less than one third of the standard of an equivalent new building (<= 33%NBS). These are high risk buildings estimated to pose 20 times the risk of buildings complying with current building standards, and must be upgraded.

Seismic risk based on percentage of New Build Standard (NBS)

eqp6

Abbreviations used:

%NBS: Percentage of standard required for new building at the time of assessment.

NZSEE Guidelines: New Zealand Society for Earthquake Engineering ‘Assessment and Improvement of the Structural Performance of Buildings in Earthquakes’.

ISA: Initial Seismic Assessment as defined in the NZSEE Guidelines.

DSA: Detailed Seismic Assessment as defined in the NZSEE Guidelines.

IEP: Initial Evaluation Procedure, a tool used as part of an ISA.

Frequently asked questions

Q:    Does this policy apply to my house?

A:    Probably not, residential buildings are not included unless they are two or more storeys high, AND have three or more household units. (See the diagram above).

Q:    Can I buy or sell an earthquake prone building?

A:    Yes, the new owner will be responsible for seismic upgrades. Buyers need to do their own investigations and seek expert advice.      

Q:    If my building has a heritage classification A or B will it need to be upgraded?

A:    The policy applies just the same as it does to other buildings. We will discuss the options with owners and NZ Historic Places Trust, and make a special effort to meet heritage objectives.

Q:    I am renovating my building. Do I have to obtain an ISA and strengthen it at this time?

A:    Not necessarily - only if a building consent is required for the renovation of a building first constructed prior to 1980. Requirements will be decided case by case. We will consider the potential risk of the building’s age, use, and value of alterations. Proposed alterations exceeding 30% of the building value will always require an ISA.

Q:    I’m changing the use of my building. Does the policy affect me?

A:    The Building Act 2004 provisions on ‘change of use’ are separate to those relating to earthquake prone buildings. A change of use requires any building to be upgraded to comply “as nearly as is reasonably practicable” with the current Building Code, regardless of its earthquake status. Guidance on preparing an application that justifies ‘nearly as is reasonably practicable’ can be found on the Ministry of Business, Innovation and Employment website.   

Q:    My building was strengthened 10 years ago as required by the Building Act 1991. Is it affected by the current policy?

A:    It probably is. The Building Act 1991 addressed buildings that posed the highest seismic risk, but the 2004 Act includes many more buildings and has increased the requirements. The NZSEE Guidelines benchmark a building’s strength against its %NBS. Further strengthening or remaining life will depend partly on the level of strengthening already carried out.

Q:    Will the policy affect insurance?

A:    Yes. Insurance policies usually require disclosure of formal notices issued regarding a building’s earthquake prone status. You should contact your insurer.

Council’s Earthquake Prone Buildings Policy Amended in 2014

Nelson City Council’s Chief Executive announced that buildings identified as earthquake prone will only be required to be strengthened to no less than 34%NBS, effective 5 March 2014.

Read about the change here.

Download

Download the full version of the Earthquake Prone Building Policy User Guide (929KB PDF).

Contact

For more information, phone Structural Engineer +64 3 545 8748 or Manager Building +64 3 546 0200.